FIG. 1 shows an example of a known subscriber line testing arrangement, wherein the subscriber line (1A) carries both normal POTS or ISDN traffic and xDSL (such as ADSL or VDSL) traffic. The arrangement according to FIG. 1 needs a splitter (3) for separating the POTS/ISDN traffic and the xDSL traffic. POTS (Plain Old Telephone Service) and ISDN (Integrated Services Digital Network) traffic are transmitted in a low frequency range while the xDSL (some Digital Subscriber Line system) traffic is transmitted in a higher frequency range. The splitter is normally a high-pass/low-pass filter, which comprises a common port (3A) for a subscriber loop, a low-pass port 3B) for a POTS/ISDN device (4), and a high-pass port (3C) for an xDSL device (5). The POTS/ISDN and XDSL devices have connections to a network.
In order for the line testing of the subscriber loop (1A) to be possible, a line tester (2) must be situated in front of the splitter before the subscriber loop from the subscriber (1) reaches the splitter, i.e. the subscriber loop is connected to the splitter through the line tester. This is due to the fact that it is impossible to measure all desired parameters through the splitter, i.e. through the high-pass or low-pass filter. It is worth noting that at subscriber's premise the loop is connected to a terminal, which also comprises a splitter.
FIG. 2 shows an example of how wiring is performed in a real implementation. Subscriber loops from subscribers (1) are connected to a MDF (Main Distribution Frame) (6), from where the subscriber loops are connected forward to the line tester (2). In the line tester the subscriber loop, which is to be tested, is connected to a test line (2D) (pair line) using a subscriber line dedicated relay (2C). A test head (2A), which is connected to the test line, performs line testing measurements. If the subscriber loop does not need to be tested the relay connects the subscriber loop back to the, MDF.
After the line tester the subscriber loop is connected from the MDF (6) to a subscriber loop dedicated splitter, more particularly into the common port (3A) of the splitter. In the splitter, the subscriber loop branches to two separate lines: a line of low frequency range and a line of high frequency range. Both lines, the line of low frequency range from the low-pass port (3B) and the line of high frequency range from the high-pass port (3C), are wired to the MDF from where they are connected to a POTS/ISDN device (4) and an xDSL device (5).
As can be noticed, the MDF connects all devices together. Thus the wiring can be multiple and when implementing it is easy to make mistakes. For helping the observing of FIG. 2 the wirings have been marked in different lines. Each device requires wiring space in the MDF, so the more devices concerning a dedicated subscriber loop are needed the less subscriber loops are possible to be connected to the MDF. It should be also noted that a line tester can handle several subscriber loops and in spite of what is illustrated in FIG. 2 the POTS/ISDN devices (4) can be one unit, which can handle several subscriber loops as well as xDSL devices (5).
The intention of the invention is to eliminate these drawbacks when making it possible to perform line testing through a splitter. Furthermore, since the splitter is a passive element it is desired to keep it passive in an arrangement according to the invention as well. The aims of the invention are achieved in a way described in the claims.